9. The current carrying capacity of cables in D.C. is more thanthat in
A.C. mainly due to
(a) absence of harmonics
(b) non-existence of any stability limit
(c) smaller dielectric loss
(d) absence of ripples
(e) none of the above
Ans: c

10. In case of three core flexible cable the colour of the neutral is
(a) blue
(b) black
(c) brown
(d) none of the above
Ans: a

In the cables, the location of fault is usually found out by comparing
(a) the resistance of the conductor
(b) the inductance of conductors
(c) the capacitances of insulated conductors
(d) all above parameters
Ans: c

26. The relative permittivity of rubber is
(a) between 2 and 3
(b) between 5 and 6
(c) between 8 and 10
(d) between 12 and 14
Ans: a

27. Solid type cables are considered unreliable beyond 66 kV because
(a) insulation may melt due to higher temperature
(b) skin effect dominates on the conductor
(c) of corona loss between conductor and sheath material
(d) there is a danger of breakdown of insulation due to the presence of voids
Ans: d

29. In cables the charging current
(a) lags the voltage by 90°
(b) leads the voltage by 90°
(c) lags the voltage by 180°
(d) leads the voltage by 180°
Ans: b

30. A certain cable has an insulation of relative permittivity 4. If the
insulation is replaced by one of relative permittivity 2, the capacitance of
the cable will become
(a) one half
(6) double
(c) four times
(d) none of the above
Ans: a

31. If a cable of homogeneous insulation has a maximum stress of 10
kV/mm, then the dielectric strength of insulation should be
(a) 5 kV/mm
(b) 10 kV/mm
(a) 15 kV/mm
(d) 30 kV/mm
Ans: b

32. In the cables, sheaths are used to
(a) prevent the moisture from entering the cable
(b) provide enough strength
(e) provide proper insulation
(d) none of the above
Ans: a

33. The intersheaths in the cables are used to
(a) minimize the stress
(b) avoid the requirement of good insulation
(c) provide proper stress distribution
(d) none of the above
Ans: c

34. The electrostatic stress in underground cables is
(a) same at the conductor and the sheath
(b) minimum at the conductor and maximum at the sheath
(c) maximum at the conductor and minimum at the sheath
(d) zero at the conductor as well as on the sheath
(e) none of the above
Ans: c

35. The breakdown of insulation of the cable can be avoided economically
by the use of
(a) inter-sheaths
(b) insulating materials with different dielectric constants
(c) both (a) and (b)
(d) none of the above
Ans: c

36. The insulation of the cable decreases with
(a) the increase in length of the insulation
(b) the decrease in the length of the insulation
(c) either (a) or (b)
(d) none of the above
Ans: a

38. In a cable the voltage stress is maximum at
(a) sheath
(6) insulator
(e) surface of the conductor
(d) core of the conductor
Ans: d

39. Capacitance grading of cable implies
(a) use of dielectrics of different permeabilities
(b) grading according to capacitance of cables per km length
(c) cables using single dielectric in different concentrations
(d) capacitance required to be introduced at different lengths to counter the
effect of inductance
(e) none of the above
Ans: a

40. Underground cables are laid at sufficient depth
(a) to minimise temperature stresses
(b) to avoid being unearthed easily due to removal of soil
(c) to minimise the effect of shocks and vibrations due to gassing vehicles,
etc.
(d) for all of the above reasons
Ans: c

41. The advantage of cables over overhead transmission lines is
(a) easy maintenance
(b) low cost
(c) can be used in congested areas
(d) can be used in high voltage circuits
Ans: c

42. The thickness of metallic shielding on cables is usually
(a) 0.04 mm
(b) 0.2 to 0.4 mm
(e) 3 to 5 mm
(d) 40 to 60 mm
Ans: a

44. Is a cable is to be designed for use on 1000 kV, which insulation
would you prefer ?
(a) Polyvinyle chloride
(b) Vulcanised rubber
(c) Impregnated paper
(d) Compressed SFe gas
(e) none of the above
Ans: d

45. If a power cable and a communication cable are to run parallel the
minimum distance between the two, to avoid interference, should be
(a) 2 cm
(b) 10 cm
(c) 50 cm
(d) 400 cm
Ans: c

46. Copper as conductor for cables is used as
(a) annealed
(b) hardened and tempered
(c) hard drawn
(d) alloy with chromium
Ans: a

47. The insulating material should have
(a) low permittivity
(b) high resistivity
(c) high dielectric strength
(d) all of the above
Ans: d

48. The advantage of oil filled cables is
(a) more perfect impregnation
(b) smaller overall size
(c) no ionisation, oxidation and formation of voids
(d) all of the above
Ans: d

49. The disadvantage with paper as insulating material is
(a) it is hygroscopic
(6) it has high capacitance
(c) it is an organic material
(d) none of the above
Ans: a

50. The breakdown voltage of a cable depends on
(a) presence of moisture
(b) working temperature
(c) time of application of the voltage
(d) all of the above
Ans: d

51. It is difficult to maintain oil filled cables.
(a) Yes
(b) No
Ans: a